Field of the Invention
Embodiments of the present invention relate generally to a charged particle beam writing apparatus and a charged particle beam writing method, and more specifically, relate to a method for achieving high-speed data processing in a writing apparatus.
Description of Related Art
In recent years, with high integration of LSI, the line width (critical dimension) required for circuits of semiconductor devices is becoming progressively narrower. As a method for forming an exposure mask (also called a reticle) used to form circuit patterns on these semiconductor devices, the electron beam (EB) writing technique having excellent resolution is employed.
FIG. 15 is a conceptual diagram explaining operations of a variable shaped electron beam (EB) writing or “drawing” apparatus. The variable shaped electron beam writing apparatus operates as described below. A first aperture plate 410 has a quadrangular aperture 411 for shaping an electron beam 330. A second aperture plate 420 has a variable shape aperture 421 for shaping the electron beam 330 having passed through the aperture 411 of the first aperture plate 410 into a desired quadrangular shape. The electron beam 330 emitted from a charged particle source 430 and having passed through the aperture 411 is deflected by a deflector to pass through a part of the variable shape aperture 421 of the second aperture plate 420, and thereby to irradiate a target object or “sample” 340 placed on a stage which continuously moves in one predetermined direction (e.g., the x direction) during writing. In other words, a quadrangular shape that can pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is used for pattern writing in a writing region of the target object 340 on the stage continuously moving in the x direction. This method of forming a given shape by letting beams pass through both the aperture 411 of the first aperture plate 410 and the variable shape aperture 421 of the second aperture plate 420 is referred to as a variable shaped beam (VSB) system (e.g., refer to Japanese Patent Application Laid-open No. 2008-218857).
Generally, in an electron beam writing apparatus, in order to enhance the data processing efficiency, a writing region where patterns are to be arranged is divided into a plurality of processing regions. Then, in the writing apparatus, a distributed processing is carried out, namely data processing of a pattern arranged in each processing region is performed in parallel. For example, since the size that can be shaped by one beam shot is limited, a figure pattern defined in writing data is divided into a plurality of shot figures each of which can be shaped by one beam shot. In that case, in shot data generation processing, if dividing is performed so that respective processing regions may be the same size, since densities of patterns arranged in the respective processing regions are different from each other, processing time greatly varies depending upon the densities. Therefore, conventionally, in order to reduce the variability of the processing time, it has been contrived to perform division so that the number of shots in each processing region may be around the same (e.g., refer to JP2008-218857A).
Meanwhile, in the electron beam writing, dimensional variation represented by the proximity effect is corrected by adjusting an irradiation amount (dose). In that case, the corrected dose is represented in a dose map which has been divided into meshes.
Regarding a writing region, there is a case in which a somewhat large region without any pattern exists. In such a case, if dividing is performed such that the number of shots in each divided processing region may be around the same, the total processing region includes the large region without any pattern. Then, when generating shot data, since a beam dose for forming a shot figure concerned needs to be defined, the beam dose should be read from the dose map. If the processing region is large, the time period to read the dose from the map is long. That is, there is accordingly a problem that the processing time for a processing region including a region where no pattern exists is longer than that for a processing region which does not include a region where no pattern exists.
Further, when calculating a correction coefficient (correction dose) for the proximity effect, etc. so as to adjust a dose, calculation processing for obtaining an area density and calculation processing for correction of the proximity effect, etc. using the calculated area density are performed. In performing the area density calculation processing and the correction calculation processing, the writing region is divided, for each processing, into a plurality of processing regions, and then, the calculation is executed for each processing region. Even in the area density calculation processing, if dividing is also performed such that the size of each processing region is the same as each other, since densities of patterns arranged in respective processing regions are different from each other, there is great variability among processing time of the respective processing regions. Therefore, conventionally, dividing is performed such that the number of shots in each processing region is around the same in order to reduce the variability of the processing time. Moreover, even in the area density calculation processing, if dividing is also performed such that the number of shots in each processing region is around the same, the total processing region includes a large region without any pattern. On the other hand, in the calculation processing for correction of the proximity effect, etc., since there is no or small amount of variability of the processing time which usually occurs due to various densities of patterns, dividing is performed so that each processing region may be the same size. However, in the proximity effect correction calculation processing, it is necessary to read a calculated area density. If the processing region of the area density calculation processing is large, with respect to the proximity effect correction calculation processing of a processing region which even partly overlaps with the large processing region of the area density calculation processing, the time period to read the area density becomes long. This consequently generates a problem in that the processing time for a processing region including a region where no pattern exists is longer than that for a processing region which does not include a region where no pattern exists.